This invention relates generally to an internal combustion engine and more specifically to operating a catalytic reactor in the internal combustion engine.
The use of fossil fuel in gas turbine engines results in combustion products in the exhaust consisting of carbon dioxide, water vapor, oxides of nitrogen, carbon monoxide, unburned hydrocarbons, oxides of sulfur, and particulates of these above products, carbon dioxide and water vapor are generally not considered objectionable.
Regulations on the remainder of emissions continue to promote innovation among engine manufacturers and researchers. Manufacturers have reduced many of the combustion products through design modifications, improved fuels, or additional hardware. Many of these changes have improved efficiencies in the engine.
However, many of these same changes have increased the production of NOx. NOx is formed by oxidation of atmospheric nitrogen. The rate of NOx production depends mostly on a temperature of combustion and to some degree upon a concentration of reactants. Consequently, a small reduction in the temperature of combustion results in significant reductions in NOx production.
Automotive engine manufacturers use exhaust gas recirculation as one method of reducing the temperatures of combustion. Exhaust gas recirculation involves replacing a volume of inlet air with combustion products. By reducing the excess oxygen, combustion proceeds at a slower rate and reduces temperatures of combustion. Additionally, less oxygen is available for oxidation of atmospheric nitrogen. While exhaust gas recirculation generally reduces the production of NOx, it also reduces the available power and generally increases fuel consumption.
Another method of controlling NOx involves injecting water or steam to reduce the temperature of combustion. This method increases cost due to additional equipment, such as pumps, lines, and a storage reservoir. Furthermore, the cost of supplying water may be cost prohibitive. In mobile applications, water further reduces efficiency by increasing the weight of the vehicle.
In a gas turbine, increasing a flow of air into a combustor reduces the temperature of combustion. This method increases excess oxygen available to oxidize atmospheric nitrogen while at the same time reducing the temperature of combustion. However, increasing the flow of air to a combustion zone tends to quench combustion causing the engine to operate unevenly. By using a low ignition temperature fuel, greater air to fuel ratios may be achieved without quenching combustion.
In U.S. Pat. No. 4,567,857 issued to Houseman et al. on Feb. 4, 1986, a fuel is reformulated in a catalytic reactor to form the low ignition temperature fuel. This invention uses exhaust gas to heat the catalyst. However, catalytic reactors only need exhaust heat for initial operation. Once operating, catalytic reactors may reach extreme temperatures nearing adiabatic flame temperatures. These high temperatures lead to vaporization of active catalyst components, sintering of the catalyst and the substrate, thermal shock of metal substrate, and fracturing of metal substrate.
In U.S. Pat. No. 5,512,250 issued to Betta et al on Apr. 30, 1996, a monolithic catalyst structure has a palladium catalyst on a first side of a substrate. A portion of the fuel air mixture is passed along a second side of the substrate to control the temperature of the substrate. The first side employs a tortuous flow path to place the flow in the greatest contact with the catalyst, and the second side is designed to maintain high flow rates which aid in cooling the substrate. This system results in reduced overall pressures and temperatures of a fuel/air mixture exiting the catalyst structure. The reduced temperatures of the fuel/air mixture limits the volume of air that may be introduced to the combustor without making the flame unstable.
The present invention is directed at overcoming one or more of the problems set forth above.
In one aspect of the present invention an internal combustion engine comprises an air inlet connected with a catalytic reactor having an inlet and an outlet. The catalytic reactor has a housing containing a thermally conductive substrate. The substrate has a first side and a second side. The first side is treated with an exothermic catalyst adapted to promote a partial catalytic combustion process of a fuel. The second side is treated with an endothermic catalyst adapted to promote cracking or reformation of the fuel. The substrate defines a network of longitudinal passages through the housing. A heating device connected between air inlet and the catalytic reactor inlet increases an air stream temperature above a temperature needed to sustain the catalytic combustion. A fuel delivery device connects between the air inlet and the catalytic reactor inlet. A combustor has an inlet and an outlet where the inlet of the combustor connects with the catalytic reactor outlet.
In another aspect of the present invention, a method of operating an internal combustion engine to reduce emissions comprises the steps of heating an air stream to a temperature above a catalytic temperature needed to sustain a catalytic combustion process. Fuel is mixed with the air stream to form a fuel/air mixture. The fuel/air mixture is exposed to a catalytic reactor having a substrate. The substrate has a first side and a second side that are thermally connected. A first portion of the fuel/air mixtures is partially combusted generating heat and a first catalytic exhaust mixture. The heat is transferred from the first side to the second side. A second portion of the fuel/air mixture is catalytically cracked or reformed on the second side of the substrate using the heat. The catalytic cracking forms a second catalytic exhaust mixture. The first catalytic exhaust mixture and the second catalytic exhaust mixture mix to form a combustible gas. The combustible gas is then combusted.
In another aspect of the invention, a method of making a catalytic reactor for use on an internal combustion engine, comprises forming a first foil having a plurality of first corrugations. The first foil has a first side and a second side. The first side of the first foil is treated with an exothermic catalyst and a first washcoat. The second side of the first foil is treated with an endothermic catalyst and a second washcoat. A first separating plate is formed having a first side and a second side. The first side of the first separating plate is treated with the exothermic catalyst and the first washcoat. The second side of the first separating plate is treated with the endothermic catalyst and the second washcoat. A second separating plate is formed having a first side and a second side. The first side of the second separating plate is treated with the exothermic catalyst and the first washcoat. The second side of the second separating plate is treated with the endothermic catalyst and the second washcoat. A second foil is formed having a second plurality of corrugations, a first side, and a second side. The first side of the second foil is treated with the exothermic catalyst and the first washcoat. The second side of the second foil is treated with the endothermic catalyst and the second washcoat. A stack is formed by attaching the first side of the first foil to the first side of the first separating plate, attaching the second side of the first foil to the second side of the second separating plate, attaching the first side of the second foil to the first side of the second separating plate. The stack is then rolled to form a cylinder wherein the second side of the first separating plate faces the second side of said second foil. The cylinder is then positioned in a housing.